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Wednesday, March 10, 2010

Revit MEP Tech Tip: Like Father...Like Son? Not Exactly - The Revit Clinic

Repost: http://revitclinic.typepad.com/my_weblog/2010/03/like-fatherlike-son-not-exactly.html

Back in the 80’s, there was a movie that came out called Like Father Like Son, starring Kirk Cameron and Dudley Moore. It was a hilarious comedy about a teenage son (Cameron) who switches bodies with his surgeon father (Moore). The laughs are unending as each of them try and figure things out in their new roles: the father trying to be cool in school and the son faking his way through the operating room.LikeFather

Did any of you see this movie?

That’s OK. I didn’t either. In fact, I should confess that the nonsense about the movie being funny came from some editorial review. I think my sister liked it, but that’s just because Kirk Cameron was in it. Whatever.

Anyway, this story of role reversal reminded me of the fundamental parent-child relationship that exists in Revit MEP mechanical systems. Most users are familiar with the general workflow of placing air terminals and mechanical equipment; creating systems; and laying out connecting ductwork. However, we occasionally receive support requests that indicate some confusion as to why this process cannot happen in reverse.

First of all, the illustration below illustrates the relationship between air terminals, VAV boxes, and the air handling unit (AHU). How were these system created? Briefly, a supply system was created using the supply air connectors on the air terminals (children). Next the VAV was added as the equipment (parent) of the supply system. Then, the (child) supply air connectors on the VAV's were used to create a second supply air system, and the AHU was selected as the equipment (parent) of the VAV's. Meanwhile, the flow is carried from the terminals right through to the AHU.


This behavior is determined by the direction of flow in the supply system in each family (IN for air terminals; OUT for VAV "parent" connector; IN for VAV "child" connector; and finally OUT for AHU). With me so far?

Well the (real) confusion comes in when users create their own equipment and discover that if they change the flow direction for one of these connectors (changing flow on AHU from OUT to IN), they can create the supply air system when they select the AHU. They mistakenly conclude that if they simply change the flow on all of the downstream families (VAV's and air terminals), a system similar to the one in the above picture can be created; only in reverse. The AHU becomes the child...and the air terminals the parent.

Well, Just like the teen Kirk Cameron had no business operating on anyone (or being in movies for that matter), neither can the air terminals serve as parent equipment on a system. In fact, if you test this out, you'll notice that you'll only be able to select one air terminal per system. No good. On the other hand, if you follow the designed workflow, the "family" will function just fine.

For those of you who stuck around to see how I could possibly tie an 80's movie in with Revit MEP, I congratulate you. I hope this overview was helpful. As I recommended in my very first post, all Revit MEP users can get a great explanation of this concept by watching Kyle's videos. Here's the link.

Now, off to watch a real movie: The Goonies Goonies_the_1985_685x385

Source: Like Father...Like Son? Not Exactly - The Revit Clinic


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